1. Field of the Invention
This invention relates to power transmission belts having alternating cog crests and cog troughs on at least one side thereof. The invention is also directed to a method of manufacturing such a belt.
2. Background Art
It is known to use belts with cog crests and cog troughs alternating along the length thereof in various systems, such as in snowmobiles, other types of vehicles, and in general industry applications. In one such system, speed shifting is effected by altering the effective diameters of driving and driven pulleys around which the belt is trained. A conventional type belt used in this environment may have the alternating cog crest and cog trough configuration on one or both sides of a belt body in a compression rubber layer and/or a tension rubber layer. Load carrying cords are commonly embedded in the cushion rubber layer between the tension and compression rubber layers.
In a conventional manufacturing process for producing this type of belt, a cog pad is preliminarily formed. The cog pad is formed from a sheet consisting of a reinforcing cloth, a non-vulcanized rubber sheet forming a compression rubber layer, and a non-vulcanized rubber sheet forming a cushion rubber layer. Cog troughs and cog crests are formed by pressing the cog sheet against a mold having a shape that is complementary to that desired, with the cog sheet at an elevated temperature. The resultant cog pad is separated and placed around a cylindrical support having slots and ridges that are complementary to the cog troughs and cog crests. The ends of the cog pad are then butt joined to produce an endless cylindrical shape. Load carrying cords, non-vulcanized sheets forming an additional cushion rubber layer and an additional tension rubber layer are sequentially applied to the cog pad, after which the entire assembly is vulcanized and thereafter cut to separate belts of desired width.
The cog pad is a lamination of one or more plies of reinforcing cloth and an unvulcanized rubber sheet which has cog crests and cog troughs spaced at a predetermined pitch along the belt length. Typically, the cog pad is manually cut to produce the desired length. It is conventional to count the number of cogs to determine the desired circumferential length of the belts and use chalk to mark the cutting positions to produce that length. The cog pad is typically cut at both of its ends at the top of a cog crest, using conventional cutting equipment.
In cutting the cog pad ends, it is desired to cut from side to side along a line that is orthogonal to the belt length. The plane of the joint at which the ends are butted is biased, i.e. non-perpendicular to a line extending along the length of the belt. If the cog pad is cut at a location spaced from a cog crest, it becomes difficult to join the ends of the cog pad to produce a straight butt line. A gap may result at the butt joint, potentially leading to volumetric cracks, and potentially making a defective joint. Thus, with this defect, there is a risk of crack formation at the joint, particularly in the event of a change of load or heat generation as the belt is running in operation.
Conventionally, the planes of the joints, made even at the cog crests, may extend to an adjacent cog trough. This can be seen on the conventional cog belt at 10, shown in FIG. 8. The belt 10 has a body 12 with cog crests (C) 14 and cog troughs (T) 16 alternating at regular intervals along the length of the belt body 12, as indicated by the doubled-headed arrow 18. A reinforcing cloth layer 20 is applied on one side 22 of the belt body 12 over the cog crests 14 and cog troughs 16. The other side 24 of the body 12 has alternating cog crests 26 and cog troughs 28, likewise alternating along the length of the belt body 12. At least one longitudinally extending load carrying cord 30 is embedded in cushion rubber layers 32,34.
In this belt 12, ends 36,38 of a rubber layer 40 are butt-connected to produce a bias joint 42 i.e. the plane thereof is non-perpendicular to a line extending lengthwise of the belt body 12. The joint 42 penetrates from a cog crest 14 to a cog trough 16, i.e. through to the region T. Rubber in the cushion rubber layer 34 tends to penetrate the trough 16 during the vulcanization process. This rubber migrates to the joint 42 at the end 44 thereof. A generally softer rubber in the cushion rubber layer 34 that has penetrated the rubber layer 40, typically a compression rubber layer, may adversely affect the integrity of the layer 40. This may result in the failure in the trough region due to fatigue resulting from repeated flexure. Cracks may generate at, or adjacent, the joint end 44 to thereby reduce the anticipated belt life. Cracks generated in the trough may propagate to the crest resulting in breakage thereof at the joint 42.
In FIG. 9, the belt 10 of FIG. 8 is shown with a joint 46, corresponding to the joint 42, wherein the joint 46 does not extend into the cog trough 16. In this embodiment, the rubber in the cushion rubber layer 34 tends to migrate into the joint 46 at the joint end 48 in the crest region. This reduces the thickness Ti of the cushion rubber layer 34 at the cog trough 16. As a result, the cog troughs 16 become more rigid, and are more prone to cracking as a result of fatigue from repeated flexing.
Short fibers in the rubber layer 40 orient, and conform to, the cog shape. With the belt 10 operated under high load, the belt side surfaces 50 (one shown) receive the sheering force from a cooperating pulleys. Crack-like grooves 52 following the cog contour may develop on the guide surfaces in contact with the pulleys. Crack-like grooves tend to also be developed at the joint 46. These grooves can potentially grow into lengthwise cracks, which may cause the belt 10 to break.
In one form, the invention is directed to a power transmission belt having a body with a length, a first side, a second side, and laterally spaced side surfaces. The body has cog crests and cog troughs in at least a first layer on the first side of the body and alternating along the length of the body. The body further has at least one cushion rubber layer and at least one load carrying cord embedded in the at least one cushion rubber layer and extending lengthwise of the body between the cog crests and the second side of the body. The at least first layer has a first joint that is in a cog crest and does not extend into a cog trough. At least one cushion rubber layer is made from a first material, with the first material from the at least one cushion rubber layer not penetrating the first joint.
In one form, there is no joint in the at least first layer that extends into a cog trough.
In one form, the at least one cushion rubber layer has a thickness between the at least one load carrying cord and the first side of the body that is substantially uniform between adjacent cog crests and cog troughs. The thickness may be uniform over the entire length of the body.
In one form, the first joint resides in a first plane that is angularly oriented to a second plane orthogonal to a line extending lengthwise of the body and extending between the first and second sides.
The first plane may make an angle of at least 60xc2x0 with respect to the second plane and may be in the range of 65xc2x0 to 90xc2x0.
The first plane may be substantially orthogonal to a line extending lengthwise of the body.
In one form, the first joint extends along a first line between the laterally spaced side surfaces, and the first line is substantially orthogonal to a second line extending lengthwise of the body.
The power transmission belt may further include a reinforcing cloth layer over the cog troughs and cog crests on the first side of the body. The reinforcing cloth has ends that are lapped at a cog crest that is spaced from the cog crest in which the first joint is formed.
The at least first layer may be a compression rubber layer.
The body may have alternating cog crests and cog troughs on the second side of the body.
The at least one cushion rubber layer may have a second joint that is spaced lengthwise from the first joint a distance equal to the spacing between adjacent cog crests.
In one form, the cushion rubber layer has the second joint that is spaced lengthwise from the first joint a distance at least equal to a spacing between adjacent cog crests.
The invention is further directed to a power transmission belt having a body having a length, a first side, a second side, and laterally spaced side surfaces. The body has cog crests and cog troughs in at least a first layer on the first side of the body and alternating along the length of the body. The body further has at least one cushion rubber layer and at least one load carrying cord embedded in the at least one cushion rubber layer and extending lengthwise of the body between the cog crests in the at least first layer and the second side of the body. The at least one cushion rubber layer has a thickness between the at least one load carrying cord and the first side of the body that does not vary between adjacent cog crests and cog troughs.
The thickness of the at least one cushion rubber layer between the at least one load carrying cord and the first side of the body may be substantially uniform over the entire length of the body.
The invention is also directed to a power transmission belt having a body with a length, a first side, a second side, and laterally spaced side surfaces. The body has cog crests and cog troughs in at least a first layer on the first side of the body and alternating along the length of the body. The body further has at least one cushion rubber layer and at least one load carrying cord embedded in the at least one cushion rubber layer and extending lengthwise of the body between the cog crests in the at least first layer and the second side of the body. The at least first layer has a first joint. The at least one cushion rubber layer has a first material, with the first material from the at least one cushion rubber layer not penetrating the first joint.
The invention is further directed to a method of manufacturing a power transmission belt with a body having a length and cog troughs and cog crests alternating along the length of the body. The method includes the steps of: forming a cog pad with first and second sides and having cog troughs and cog crests on the first side and first and second spaced ends; joining the first and second spaced ends at a first joint to produce an endless configuration; applying a cushion layer with first and second spaced ends against the second side of the cog pad and joining the first and second ends of the cushion layer at a second joint that is spaced lengthwise relative to the body from the first joint; wrapping a load carrying cord against the cushion layer; applying a second cushion layer over the load carrying cord; and vulcanizing the cog pad and cushion layers.
A rubber layer may be applied over the second cushion layer.
The first joint may reside entirely within a cog crest.
In one form, the second joint is spaced from the first joint by a distance at least equal to spacing between adjacent cog crests.
The method may further include the step of cutting the cog pad and cushion layers to a desired width after vulcanization.
The invention is further directed to a method of manufacturing a power transmission belt having a body with a length and cog troughs and cog crests alternating along the length of the body. The method includes the steps of: forming a cog pad with first and second sides and having cog troughs and cog crests on the first side and having first and second spaced ends; joining the first and second spaced ends at a first joint to produce an endless configuration, the first joint residing entirely within a cog crest; applying a cushion layer against the second side of the cog pad so that no joint in the cushion layer coincides with the first joint along the length of the body; wrapping a load carrying cord against the cushion layer; applying a second cushion layer over the load carrying cord; and vulcanizing the cog pad and cushion layers.